Many of the regulatory peptides that are important in maintaining nutritional homeostasis are found in the gastrointestinal environment. These peptides may be synthesized in the digestive system and act locally, but can also be identified in the brain as well. In addition, the reverse is also found, i.e., peptides are synthesized in the brain, but found to regulate cells in the gastrointestinal tract. This phenomena has been called the xe2x80x9cbrain-gut axisxe2x80x9d and is important for signaling satiety, regulating body temperature and other physiological processes that require feedback between the brain and gut.
The gut peptide hormones include gastrin, cholecystokinin (CCK), secretin, gastric inhibitory peptide (GIP), vasoactive intestinal polypeptide (VIP), motilin, somatostatin, pancreatic peptide (PP), substance P and neuropeptide Y (NPY), and use several different mechanisms of action. For example, gastrin, motilin and CCK function as endocrine- and neurocrine-type hormones. Others, such as gastrin and GIP, are thought to act exclusively in an endocrine fashion. Other modes of action include a combination of endocrine, neurocrine and paracrine action (somatostatin); exclusively neurocrine action (NPY); and a combination of neurocrine and paracrine actions (VIP and Substance P). Most of the gut hormone actions are mediated by membrane-bound receptors and activate second messenger systems. For a review of gut peptides see, Mulvihill et al., in Basic and Clinical Endocrinology, pp.551-570, 4th edition Greenspan F. S. and Baxter, J. D. editors., Appleton and Lange: Norwalk, Conn., 1994.
Many of these gut peptides are synthesized as inactive precursor molecules that require multiple peptide cleavages to be activated. The family known as the xe2x80x9cglucagon-secretinxe2x80x9d family which includes VIP, gastrin, secretin, motilin, glucagon and galanin exemplifies peptides regulated by multiple cleavages and post-translational modifications.
Motilin is a 22 amino acid peptide found in gut tissue of mammalian species (Domschke, W., Digestive Diseases 22(5):454-461, 1977). The DNA and amino acid sequences for porcine prepromotilin have been identified (U.S. Pat. No. 5,006,469). Motilin has been identified as a factor capable of increasing gastric motility, affecting the secretory function of the stomach by stimulating pepsin secretion (Brown et al., Canadian J. of Physiol. Pharmacol. 49:399-405, 1971), and recent evidence suggests a role in myoelectric regulation of stomach and small intestine. Cyclic increases of motilin have been correlated with phase III of the interdigestive myoelectric complex and the hunger contraction of the duodenum (Chey et al., in Gut Hormones, (eds.) Bloom, S. R., pp. 355-358, Edinburgh, Churchill Livingstone, 1978; Lee et al, Am. J. Digestive Diseases, 23:789-795, 1978; and Itoh et al., Am. J. Digestive Diseases, 23:929-935, 1978). Motilin and analogues of motilin have been demonstrated to produce contraction of gastrointestinal smooth muscle, but not other types of smooth muscle cells (Strunz et al., Gastroenterology 68:1485-1491, 1975).
The present invention is directed to a novel secreted protein with homology to motilin, found to be transcribed in the gastrointestinal system. The discovery of this novel peptide is important for further elucidation of the how the body maintains its nutritional homeostasis and development of therapeutics to intervene in those processes.
Within one aspect, the present invention provides an isolated polynucleotide molecule encoding a polypeptide selected from the group consisting of: (a) polynucleotide molecules comprising a nucleotide sequence as shown in SEQ ID NO: 1 from nucleotide 70 to nucleotide 111; (b) allelic variants of (a); (c) polynucleotide molecules that encode a polypeptide that is at least 60% identical to the amino acid sequence of SEQ ID NO: 2 from amino acid residue 24 to amino acid residue 37; and (d) degenerate nucleotide sequences of (a), (b) or (c).
Within another aspect, the present invention provides an isolated polypeptide selected from the group consisting of: (a) polypeptide molecules comprising an amino acid sequence as shown in SEQ ID NO: 2 from residue 24 to residue 37; (b) allelic variants of (a); and (c) polypeptide molecules that are at least 60% identical to the amino acids of SEQ ID NO: 2 from amino acid residue 24 to amino acid residue 37.